The metal containers that are handled by the device of this invention are made from metal extruded, deep-drawn or deep-drawn/ironed metal rough pieces, of aluminium, its alloys or other suitable materials; these containers, can be painted inside and/or outside and lithographed along the outer side surface before starting the sequence of operations that deform their external side surface
These metal containers mainly undergo plastic deformation processes that are aimed at changing their geometrical structure in a partial manner (the so-called “necking” or “tapering” process), in a global manner (the so-called “shaping” process) or by making hollow or embossed shaped marks on pre-set portions of the side surface of the metal container (“embossing/debossing” process).
It is known that in high-speed machines, the metal container is transferred from one working tower or station to another in order to perform the sequence of working operations on its outer side surface.
The transfer stage of metal containers from one working station to the one coming next is particularly critical, since their transport system should allow a safe grip to avoid losing the container, but the grip also has to be sufficiently soft to avoid damaging the side surface of the metal container.
In metal container continuous-working machines, namely those working the above-described containers, in the shape of cans or “pop cans” and preferably addressed to the beverage market, the grip directly occurs along the cylindrical section of the side surface of the metal container, both at the transfer and the working stages, by means of slots or “pockets” wherein a vacuum degree is created such as to allow the above container to be gripped.
However, this type of grip for handling metal containers presents problems of great relevance.
During the transfer from one working station or tower to the one coming next, the metal container is diverted and secured for a short length on the working tower coming after the one that has been left, by means of special guides so as to allow the gripping means or “receiving pocket” to reach a sufficient vacuum degree. These guides come into contact with the side surface of the metal container, so as to produce some dragging that is likely to damage the side surface of the container.
A further problem stands in that the foregoing contacts or dragging, already hinted at above, tend to alter the angular position of the metal container; indeed, the angular position of the metal container as to its longitudinal axis is not controlled and may vary during the transfer from one working tower to the one coming next.
Another problem is that the gripping of the metal container strongly relies on the quality of the structure of its surface; an outer side surface bearing defects makes it difficult to high-speed handle the metal container due to “leaks” that reduce the vacuum degree grid, hence, the strength that may be exerted on the surface.
Another disadvantage stands in that the chance of losing/damaging the metal container during the transfer stage from one working station to the one coming next increases in proportion to the number of operations carried out on the container and, therefore, to the complexity of the shape achieved, since contact with the side surface of the container recurs at each transfer.
Further disadvantageous is that the described handling system only allows handling metal containers whose outer side surface presents an extensive cylindrical section, as the grip by the vacuum technique only proves to be effective if action is taken on an extended portion of the outer side surface of the metal container. This cylindrical segment must not be smaller than approximately 70÷80% the outer side surface of the metal container.
However, the market is currently oriented to the high-speed production of metal containers in the shape of “bottle cans” and/or “contour cans” that are machined on almost the entire outer side surface; these containers have a limited cylindrical length and demand, for their working, a large number of passages.
Accordingly, the vacuum gripping technology for the direct transfer of the metal container from one working station to the one coming next proves to be unsuitable to guarantee a safe, accurate and firm gripping of the container itself.